Backgrounds: Despite dual anti-platelet therapy, the rate of major adverse cardiovascular events (MACE) after percutaneous coronary angioplasty remains high. Studies have shown inter-individual variations in response to clopidogrel. Furthermore, there is an apparent link between clinical outcomes and clopidogrel resistance. This study is to assess whether low response to clopidogrel influences cardiovascular outcome after coronary stenting in a consecutively measured cohort of Korean patients. Methods: A total of 105 consecutive patients with symptomatic coronary artery disease (CAD), [stable angina n=52, acute coronary syndrome (ACS) n=53] treated with percutaneous coronary stenting were enrolled. Responsiveness to aspirin and clopidogrel was assessed by VerifyNow짰 Aspirin test and VerifyNow짰 P2Y12 test respectively, after administration of a loading dose of 600 mg clopidogrel. ARU>550 defined as aspirin resistance and platelet inhibition < 40% was defined as low response to clopidogrel. The prevalence of aspirin and clopidogrel resistance was compared in stable angina and ACS group. During 6 month follow-up, the primary outcome of a combined MACE was evaluated. Results: 13 patients (12.4%) were aspirin resistance and 43 patients (40.9%) were classified as low responders to clopidogrel. In comparing with stable angina and ACS group, there was no significant difference of prevalence of clopidogrel resistance (23/52 in stable angina and 20/53 in ACS, p=0.36) During follow up, compared in both group with patients who adequately responded to clopidogrel, a low responder had a significantly higher risk of in-stent restenosis (ISR) and target lesion revascularization (9/43 vs. 1/62 p<0.01). There was no death or fatal MI in both groups. Conclusions: The prevalence of clopidogrel resistance in Korean patients was relatively high in our data. Low response to clopidogrel in patients with symptomatic CAD treated by stenting significantly enhances the occurrence of ISR. The evaluation of low response to clopidogrel may help to identify patients at increased risk who may benefit from intensified antiplatelet strategy.